Active supermassive black holes often produce powerful jets of ionized gas that race away from their host galaxies. These jets can be seen using radio telescopes as radiolobes. Active galaxies can have one or two radiolobes, and when they have two they are known as bilobed radio sources associated with active galactic nuclei, or DRAGN. The jets of most DRAGNs are symmetrical, but some are not. These asymmetric DRAGNs could tell us a lot about galaxies and their surroundings, but identifying them can be a challenge.
Kavita Gosine Bissessar, a student at the University of the West Indies, wanted to find these asymmetric DRAGNs, so she started with a catalog of 17,724 DRAGNs captured by the Very Large Array Sky Survey (VLASS). She combined this with infrared data from the Wide-Field Infrared Survey Explorer (WISE) to identify its host galaxies. From this, Kavita discovered that 1,587 of them had confirmed galactic nuclei.
But to find out which ones were asymmetrical, Kavita had to comb them by hand. She started by measuring the arm-to-core distance ratio, since DRAGNs with larger ratios are more likely to be symmetrical. She found that 33 of them had ratios greater than 3.6. Interestingly, she found that those with the largest proportions appeared asymmetrical, but were actually false positives. Some were actually two separate galaxies, while others had bright radio nuclei mistakenly identified as a lobe. Kavita found that DRAGNs with arm-to-core distance ratios between 3 and 8 had the highest probability of being true asymmetric DRAGNs.
This result may help astronomers find galaxies with asymmetric radio lobes more easily. In the future, Kavita would like to study the environments of these galaxies to see how this might affect the symmetry of the galactic lobes.
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